A development trend of mobile communications is a broadband technology. Currently, a multiple-input multiple-output (Multiple-Input Multiple-Output, MIMO) technology is mainly used to improve system bandwidth. The MIMO technology needs to be supported by a multi-antenna technology. Currently, an eight-antenna technology has been used commercially, and with the appearance of fifth-generation mobile communications technologies, a larger-scale antenna array will appear. In this case, an ultra-large-scale antenna array that follows causes a rapid increase in a quantity of radio frequency channels in an ultra radio frequency system. Therefore, how to simplify a radio frequency system and how to reduce a quantity of radio frequency components in the radio frequency system are main design directions of a future radio frequency system.
As main components of a radio frequency channel, an analog to digital converter (Analog to digital converter, ADC) and a digital to analog converter (Digital to analog converter, DAC) are very expensive.
In the prior art, in a reception direction of a radio frequency system, an intermediate frequency combination technology is used to reduce a quantity of ADCs, that is, a received radio frequency carrier signal is down-converted by using a mixer, to move the radio frequency carrier signal to an intermediate frequency, and radio frequency carrier signals received on multiple channels are combined into a channel of broadband signal, so that sampling can be performed by using only one high-speed ADC, thereby reducing the quantity of ADCs. However, because intermediate frequency bandwidth is limited, a quantity of channels that can be combined is limited by the intermediate frequency bandwidth. Currently, the intermediate frequency bandwidth is usually less than 1 GHz, but in future wireless communications, bandwidth of each channel will exceed 400 MHz. Therefore, the foregoing intermediate frequency combination technology supports combination of two channels at most, a quantity of ADCs is reduced by half at most, and a quantity of reduced ADCs is very limited.